1. Field of the Invention
The invention relates to a vehicle and a control method thereof. More specifically, the invention relates to a vehicle having an automatic shutoff function in which the internal combustion engine can be shut off when the vehicle speed detected by vehicle speed detecting means falls into a first low vehicle speed region, as well as to a control method of that vehicle.
2. Description of the Related Art
One known vehicle provided with an internal combustion engine performs control to suppress catalyst degradation in order to suppress degradation of an exhaust gas control catalyst that purifies exhaust gas discharged from the internal combustion engine by prohibiting a fuel cut when the temperature of the exhaust gas control catalyst is in a high temperature region. For example, Japanese Patent Application Publication No. JP-A-2005-147082 describes a vehicle in which, at the start of executing the control to suppress catalyst degradation, the condition for executing that control is a condition in which the vehicle speed is equal to or greater than a predetermined value set in advance. This predetermined value is set to a low vehicle speed at which an occupant is able to smell the sulfurous odor of hydrogen sulfide, which is discharged from the tailpipe when the control to suppress catalyst degradation is executed, in the air around the vehicle. Therefore, when the vehicle speed is less than the predetermined value, priority is given to not subjecting the occupant to the sulfur smell over suppressing catalyst degradation.
In the vehicle having this automatic shutoff function in which the internal combustion engine shuts off in the low vehicle speed region, if the control to suppress catalyst degradation is executed in that low vehicle speed region, the user may feel odd because the internal combustion engine keeps firing (i.e., continues to operate) under conditions in which the internal combustion engine should normally shut off. Accordingly, it is of course possible to prohibit the control to suppress catalyst degradation from being executed when the vehicle speed is less than the predetermined value set in advance, as with the vehicle described in Japanese Patent Application Publication No. JP-A-2005-147082, but in this case, even though the user would feel less odd, degradation of the catalyst would not be suppressed, which may shorten the life of the catalyst.